Steel Fiber Reinforced Mortar Research Articles

Experimental Study of Solid and Hollow Clay Brick Masonry Walls Retrofitted by Steel Fiber-Reinforced Mortar Coating

ABSTRACTAn experimental study including reverse quasi-static cyclic tests on solid and hollow Unreinforced Masonry walls strengthened with thin steel fiber-reinforced mortar (SFRM) coating is herein presented. Three types of mortars containing nano-silica and three different typologies of short high-strength steel fibers are used.Compared to traditional coating techniques, the proposed strengthening method adopts a thin layer (25 mm tick) of SFRM anchored on the wall surface by means of steel connectors.Results show that this novel technique provides significant enhancement in terms of strength and stiffness. Critical considerations on the in-plane lateral resistance of masonry walls are reported.

소성힌지부 강섬유 혼입 모르타르 적용 철근콘크리트 기둥의 내진성능평가

이 연구에서는, 철근콘크리트 기둥 실험체를 대상으로 기둥의 휨 위험 단면부에 국부적으로 강섬유 시멘트 모르타르를 적용함으로서 기존 철근콘크리트 기둥에 비해 내진성능이 우수한 강섬유 모르타르 적용 철근콘크리트 복합기둥공법에 관해 제시하였다. 제시된 적용공법의 성능검증을 위하여 기존 철근콘크리트 기둥 1개 및 소성힌지 구간에 국부적으로 강섬유 모르타르를 적용한 복합기둥 실험체 2개를 제작하여 일정 축하중 하에서 횡방향 반복하중을 받는 재하시험을 수행하였다. 콘크리트 및 강섬유 모르타르는 모두 현장타설되었다. 재하시험 결과 기존 철근콘크리트 기둥 실험체와 비교하여 강섬유 모르타르 적용 철근콘크리트 복합기둥 실험체의 경우 휨 및 전단 균열의 제어에 우수할 뿐만 아니라 기둥의 횡하중 내력 및 횡방향 변형 능력 향상에서도 우수한 것으로 평가되었다.

Study of interfacial microstructure, fracture energy, compressive energy and debonding load of steel fiber-reinforced mortar

The properties of the interfacial transition zone (ITZ) of steel fiber and the bulk matrix were quantified using the backscattered electron imaging analysis (BSE-IA) and the scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX), and their relationship with the mechanical properties of steel fiber-reinforced mortars was studied. The water and binder ratio (w/b) of mortar, the amount of silica fume and steel fiber were varied. From the quantitative analysis, a higher build-up of calcium hydroxide was found from the steel fiber’s interface up to 2 or 4 μm distance away and its build-up was reduced with the 10% cement replacement by silica fume. Porosity in the ITZ and bulk matrix decreased the fracture energy, compressive energy and debonding load of steel fiber-reinforced mortar. However, its effect became marginal if a substantial amount of C–S–H or steel fibers appeared in the ITZ and bulk matrix, which increased the studied mechanical properties.

Use of steel fiber reinforced mortar for seismic strengthening

The objective of this research was to develop an economical, structurally effective, and practically applicable steel fiber reinforced mortar (SFRM) which could be applied onto the hollow brick infills of a reinforced concrete (RC) structure. Masonry walls were almost converted into strong and rigid infills with the application of SFRM. Two different mix proportions were produced with the composition of Portland cement, fine aggregate, water, and plasticizer or bonding agent as the chemical admixture. Tests were carried out to determine the optimum steel fiber content (1%, 2%, or 4% by volume) and to clarify the use of plasticizer or bonding agent in the mortar in the context of sticking ability, flexural, compressive, and adhesion strengths. As a result, mortar with plasticizer and 2% steel fiber (by volume) came out to be the optimum mortar mixture as strengthening material. The performance of RC frame strengthened with SFRM containing plasticizer and 2% steel fiber by volume was compared to those of the hollow brick infilled RC frame without strengthened mortar and the hollow brick infilled RC frame with reference mortar. It was observed that the specimen strengthened with the optimum mortar mix satisfied the target objectives of this study.

A Computational Approach to Investigate Electromagnetic Shielding Effectiveness of Steel Fiber-Reinforced Mortar

A Computational Approach to Investigate Electromagnetic Shielding Effectiveness of Steel Fiber-Reinforced Mortar

鋼繊維補強モルタルの耐久性に関する研究

Steel fiber reinforced mortar (SFRM), a composite material by compounding the short steel fibers in mortar uniformly, is considered to improve the resistance against the defect of cracks and toughness in plain mortar. SFRM is now getting more popularity in the application field of construction. The evaluation of durability and service life is important in wide ranges of application. However, only limited information is known concerning the durability of SFRM.In this study, three sites were chosen to investigate the durability of SFRM. The first site is a tunnel in Garou mine (Hokkaido) where SFRM lining was sprayed 18 years ago. The steel fibers were found to be almost sound except the rusted fibers on/near the wall surface. The tensile and compressive strengths were found to be close to the initial values obtained 18 years ago.The second site is a slope in Shizuoka Prefecture where plain mortar and SFRM were sprayed in 1994. Investigation of the slope in 1997 showed that mean crack-width on SFRM was considerably smaller than that on plain mortar. The number of cracks on SFRM was only 1/3 of that on the plain mortar.The third site is seashore in Chiba Prefecture and exposure tests were started in 1996. The compressive strength of SFRM did not change so much for five years. Thereafter, the strength decreased considerably.

インデント型鋼繊維の引抜抵抗に関する研究

Steel fiber reinforced mortar(SFRM) or concrete(SFRC) is one of the future promising composite materials and suits, for example, today's rapid excavation by a tunnel boring machine, a boom header or a continuous miner.It is well known that SFRM is improved in toughness and crack resistance mainly by the pullout resistance of steel fibers. Though some pullout tests have been published, fundamental data concerning pullout resistance are still insufficient.In this study, pullout tests were conducted pulling an indent-type steel fiber out of the mortar sample at a constant displacement rate by a servo-controlled testing machine. It was found that load-displacement curves obtained experimentally were not smooth with complicated shapes especially in the post-failure region (region after the maximum pullout resistance). The curves were classified into four patterns depending on the shapes. For every pattern, the maximum pullout resistance and the total pullout energy necessary to pull the steel fiber out of the mortar sample were obtained. Finally, the correlation between the maximum pullout resistance and the tensile strength of SFRM were discussed.

吹き付けた鋼繊維補強モルタルの一軸圧縮応力下での挙動

Steel-fiber-reinforced mortar (SFRM) or concrete (SFRC) is one of the future promising composite materials. SFRM can be sprayed easily and quickly on the wall of tunnel or gateway. Sprayed SFRM is especially suitable to today's rapid excavation by a tunnel boring machine, a boom header or a continuous miner.In this study, uniaxial compression tests were performed controlling strain rate in air-dried condition. It was found that steel-fibers did not affect the peak strength and the pre-failure characteristics such as Young's modulus and Poisson's ratio.It is well known that a sprayed steel fiber is oriented parallel to the sprayed surface. When load was applied in the fiber oriented direction, no apparent effect of steel fibers was observed even in the post-failure region. When load was applied perpendicular to the fiber oriented direction, on the contrary, ductility and residual strength in the post-failure region considerably increased. An empirical equation was proposed to estimate the residual strength. Also, energy required to break a SFRM sample was obtained and discussed.